<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .container{
            width: 300px;
            height: 200px;
            border: 1px solid #ccc;

            /* 尺寸调节 */
            resize: vertical;
            overflow: auto;

            /* 盒子阴影 */
            box-shadow: 10px 10px 5px 3px #ccc inset;
        }
        .container div{
            width: 100px;
            height: 200px;
            float: left;

            border: 1px solid blue;

            /* 此时盒子的width和height会包含border和padding */
            box-sizing: border-box;
            padding: 10px;
            /* 不包含margin */
            /* margin: 5px; */
        }

    </style>
</head>
<body>
    <div class="container">
        <div>div1</div>
        <div>div2</div>
        <div>div3</div>
    </div>

</body>
</html>